1. Field of the Invention
The invention relates generally to a fluid collecting device for use when disconnecting pipes and in particular to a mud bucket for use in the oil production industry.
As is well known, borehole drilling is generally carried out by means of a drill bit at the end of a string of hollow sections of pipe which are joined by tapered threaded connections. The connections are sufficiently strong to transmit the linear, torsional and bending forces involved in drilling and also provide a mechanical seal to prevent leakage of the drilling mud which is pumped down the drill string to lubricate the bit, balance hydrostatic pressure in the rock formation, and carry the cuttings back to the surface.
Drilling mud can contain a variety of chemicals, and for cost, environmental and safety reasons it is desirable that spillage of mud in the drilling rig should be kept to a minimum. Drill pipes are generally connected together in approximately 27-meter long “stands” consisting of three 9-meter lengths. Depending on its internal diameter, each stand can contain a considerable amount of mud. For example, the internal volume of 27 meters of pipe with a mean internal diameter of 63.5 mm is 85.5 liters.
When withdrawing the drill string from a hole, a large proportion of the mud can remain in the drill pipes and would escape when each stand was disconnected unless measures where taken to prevent this from happening. A device commonly used to contain leakage is referred to as a mud bucket and basically consists of shells which are clamped around the drill pipe connection when it has been sufficiently loosened that further rotation requires relatively little torque, but significant leakage has not occurred. A hose is led from the mud bucket to a holding tank to enable the mud collected in the mud bucket to be returned to the holding tank. A mud bucket can be deployed either by suspension from a wire connected to a hoist, or can be automatically moved into position by mechanical arms and other robotic devices.
The shells of a mud bucket are fitted with elastomeric seals to provide a leakage-free fit at the joints with each other and the drill pipe. The shells of the mud bucket may be clamped or closed around the drill pipe manually or by hydraulic or pneumatic actuators. Regardless of the clamping method employed, the shell closing mechanism must be capable of resisting the large force resulting from the pressure exerted by the mud column on the shells. Each meter of mud in the column equates to a pressure of about 0.1 bar when the specific gravity is 1.0. The force on each half of the shell is equal to the projected area multiplied by the total pressure. For example, if the internal diameter of the shells is 300 mm, the height 1.5 meters and the mud column 10 meters, the force on the shells is about 44,000 newtons or 4.4 metric tons.
2. Description of the Prior Art
GB 2300659 describes a mud bucket comprising a can which is longitudinally split into two sections. Each section is provided with a seal along the split, and the two sections are hinged together at a common pivot point. Each section is further connected to an actuator which moves the mud bucket between an open and closed position.
However, in the mud bucket described in GB 23003659, the perpendicular distance between the actuator and the common pivot point between the two sections decreases as the device closes, so that the leverage available to the actuator to close the mud bucket is decreased in the very time at which it is desirable for it to be increased. This means that larger actuators have to be used, or some subsidiary mechanical or hydraulic locking mechanism employed to prevent leakage caused by the internal mud pressure.
All drill pipes are joined together using male and female threads cut into larger diameter sections (or tool joints) at each end. The threads are then tightened up to a very high torque to withstand the linear, torsional and bending forces involved in drilling.
When drill pipe is removed from the bore hole, it is customary to loosen the high torque of the tool joints with two tongs, which can be either manually or hydraulically operated, so that further rotation requires relatively little torque. At this stage little or no mud is leaking from the tool joints, and the mud bucket is clamped around the drill pipe tool joints. Once the mud bucket is installed, a separate hydraulic or pneumatic pipe spinner (or spinning wrench) is used to revolve the upper pipe stand for a number of full turns, and therefore complete the loosening of threads of the tool joints. The spinner rotates the upper drill pipe stand by means of motor driven rollers or chains, while the lower drill pipe is prevented from rotating by the tapered slips used to hold it in position. The upper stand in than lifted up a few centimeters to allow the drilling mud to drain into the mud bucket and through the drain hose to a holding tank.
On manual drilling rigs the pipe spinner is swung into location on the pipe above the mud bucket on a hanging wire attached to a winch by personnel who often have to climb onto the mud bucket to complete the operation. This can be dangerous for personnel if the mud bucket is positioned at an awkward height above the drill floor.
On automatic and semi-automatic drilling rigs it is customary to use a hydraulically powered and positioned device called an iron roughneck that employs a pair of tongs and a pipe spinner, one of whose functions is to provide the loosening and spinning functions described above. Newer models of this device are fitted with an integral mud bucket that can be clamped around the tool joints prior to the final loosening of the tool joints with the device's integral pipe spinner. Older models of this device are not fitted with a mud bucket, and it is not possible for a separate mud bucket to be deployed during the spinning function. This results in significant mud loss onto the drill floor before the separate mud bucket can be deployed.
U.S. Pat. No. 4,643,259 describes a hydraulic drill string breakdown and bleed-off unit which includes a hydraulic drill string disassembly apparatus in combination with a pressure chamber for bleeding off trapped pressure in the drill pipes and a further apparatus for collecting drilling mud from the drill pipes. The unit described in U.S. Pat. No. 4,643,259 employs two tongs for loosening the torque of the tool joints of the drill pipes and is large, heavy, slow, cumbersome and expensive to manufacture.
3. Identification of Objects of the Invention
An object of the invention is to overcome the problems of the prior art by providing a fluid collecting device designed and arranged such that the mechanical advantage of the closing actuator increases as the bucket moves from an open to a closed position.
Another object of the invention is to provide a fluid collection device having an actuator attached to a rigid frame.
Another object of the invention is to provide a fluid collection device housed within a supporting framework to provide operator safety.
Another object of the invention is to provide a fluid collection device in combination with a pipe spinner, housed within a common framework.